Anyone who had never entered that crevice would be nervous about what would be on the other side, or rather, nervous about just getting close.
There was a sort of invisible pressure in the surroundings, and a feeling of stagnation and suffocation began to form the closer you got. If I had to describe it, it was like getting really close to a big flare, but without the heat factor.
While it was my first time as well, I wasn't nervous at all. The memories of my alternate self, where I entered or exited these crevices were so many and so numerous that I felt like I had done it many times before.
When I came in contact with the portal, I felt like I was in between something liquid, but at the same time intangible like fog, it was strange.
You could feel it with your skin as if it were a liquid, but at the same time the sensation was so faint that it could very well be a hallucination.